This project involves research on two serologically complex hematopoietic-lymphoid cell surface antigens, chicken fetal antigens (CFA) and chicken adult antigens (CAA). CFA and CAA are differentially expressed during cell differentiation and chicken development and represent useful membrane markers for studying normal in vivo hematopoietic-lymphoid differentiation/maturation pathways (i.e., pathways of erythrocytes, macrophages, monocytes, B and T lymphocytes). CFA and CAA are also useful membrane markers for defining and studying the target cells and transformed cell states of retrovirus infections. In avian erythroblastosis virus (AEV)-transformed erythroleukemic cells, CFA and CAA are important markers in defining the altered state of differentiation in which these cells are blocked and are useful in following differentiation of erythroleukemic cells that have been induced with various chemicals to break the blocked state of differentiation. As with the AEV-transformed cell system, CFA and CAA are being used to examine the blockage in differentiation theory of cancer in reticuloendotheliosis virus (REV)-transformed immature lymphoid cells. Recent studies have involved the molecular characterization of CFA and CAA and have shown them both to be composed of several different molecular weight glycoproteins. The role of CFA and CAA in normal cellular differentiation and neoplastic cell blockage as well as the involvement of CFA as viral receptors and viral product binding sites is currently under investigation.